Cartilage acts as a pad between bones to reduce friction and prevent the bones from grinding against one another. Over time, due to injury and/or heredity, however, lesions such as fissures, cracks or crazes can form in the cartilage. In some cases, osteochondral, the lesion penetrates to the subchondral surface of the bone. In other cases, chondral, the lesion does not penetrate to the subchondral surface of the bone.
One past approach for regenerating new cartilage has been autologous chondrocyte transplantation. Other techniques, aimed at repair instead of regeneration, have included debridement, lavage, microfracturing, drilling, and abrasion arthroplasty. These procedures generally involve penetrating the region of vascularization in the subchondral bone with an instrument until bleeding occurs. Formation of a fibrin clot differentiates into fibrocartilage, which then covers the defect site. A further alternative approach has been to undergo a total replacement of the joint.